Even the party’s moderate senators are now pushing for the same kind of public health insurance option that their centrist predecessors killed in the early Obama years. And the party’s 2018 platform — the consensus agenda that ostensibly unites all Democrats, from Joe Manchin of West Virginia to Bernie Sanders — calls for vigorous antitrust enforcement to prevent mega-corporations from rigging the economy against working people.

The party’s resident “sensible centrists” are horrified: “Has the entire Democratic Party forgotten the words ‘George McGovern’?” they cry. In column after column, they have been imploring their co-partisans to remember a fundamental fact: America is a center-right nation, where nearly 70 percent of voters are moderate or conservative, and just 25 percent are liberal. Over the past eight years, Democrats lost sight of this inconvenient truth — and lost control of more than 1,000 state legislative seats, the House, the Senate and the presidency.

This argument may sound coolheaded and pragmatic. But its core premises — that American voters are hostile to progressive economics and have punished the (increasingly left-wing) Democratic Party accordingly — actually rest on ideological conviction, not empirical evidence.

In truth, the Republican Party’s dominance has little to do with the American electorate’s “center-right” ideology. We know this for two simple reasons: First, the vast majority of that electorate has no ideology, whatsoever. And second, when polled on discrete policy questions, Americans consistently express majoritarian support for a left-of-center economic agenda.

The political scientist Philip Converse first brought the first reality to national attention in 1964. In his classic essay “The Nature of Belief Systems in Mass Publics,” Mr. Converse demonstrated that only 17 percent of American voters could both correctly assign the terms “liberal” and “conservative” to the nation’s two major political parties and offer a sensible description of what those terms meant. The rest of the electorate did not understand politics as a fight over abstract theories of good government but rather a conflict between interest groups. Ordinary voters did not select the party that most faithfully represented their political philosophy — they picked the one that appeared to best represent their people, a group they might define with reference to class, region, religion, race or partisanship itself.

This make intuitive sense: The left-to-right political spectrum is a construct born of seating arrangements during the French Revolution. The impulse to define oneself in relation to an in-group — and opposition to an out-group — is a survival strategy that’s been with us since the dawn of our species.

And in their recent book “Neither Liberal Nor Conservative: Ideological Innocence in the American Public,” the political scientists Donald Kinder and Nathan Kalmoe show that the electorate is scarcely more ideological today, at the peak of partisan polarization, than it was at the height of the New Deal consensus (when Mr. Converse published his landmark study).

Thus, while it’s true that fewer Americans self-identify as liberal than as moderate or conservative, this tells us almost nothing about voters’ policy views. “Moderates” do not actually display a preference for “centrist” positions, but merely for ideologically inconsistent ones. In fact, the Stanford political scientist David Broockman has shown that moderates are just as likely to subscribe to “extreme” policy positions as other voters are: In the United States, there are self-identified “moderates” who support a $1 million maximum income, prohibiting gays and lesbians from teaching public school and the mass deportation of all undocumented immigrants.

Meanwhile, the number of genuine “liberals” and “conservatives” is far smaller than meets the eye. Most voters who identify with those terms are partisans first, and ideologues second. Or as Mr. Kinder and Mr. Kalmoe conclude an analysis of four decades of voter survey data, “ideological identification seems more a reflection of political decisions than a cause.” In other words: The average conservative Republican isn’t a Republican because she’s a conservative — she self-identifies as a conservative because she’s a Republican.

One crucial implication of this finding is that political elites have enormous power to dictate ideological terms to their rank-and-file supporters. For a healthy chunk of conservative Republicans and liberal Democrats, the “liberal” and “conservative” position on most issues is whatever their party leaders say it is. Donald Trump’s success at redefining conservative voters’ consensus views on free trade, Americanpolicy toward Russia and the relevance of personal morality to effective political leadership offers a particularly vivid illustration of this phenomenon.

When we look past ideological self-identification to polling on discrete public policy questions, America appears to be far more center-left than center-right. In a recent analysis of Democracy Fund Voter Study Group survey data, the political scientist Lee Drutman found that 73.5 percent of the 2016 electorate espoused broadly left-of-center views on economic policy.

The Democratic Party has failed to translate the popularity of progressive economics into electoral success for a variety of reasons. The most fundamental is the one we’ve already observed: Most voters cast their ballots on the basis of identity, not policy. And America’s rapidly changing demographics — and the right’s steadfast efforts to inflame and exploit anxieties about those changes — have made racial identity increasingly salient to white voters, particularly rural ones. This development, combined with the disproportionate influence that our political system awards to white rural voters, has given Republicans a structural advantage.

Democrats have all kinds of ways of addressing this problem. One would be to cultivate the class identity of white voters by embracing populist rhetoric that paints “the billionaire class” as an out-group they can define themselves against. Another would be to invest more resources into registering nonwhite voters. According to the Census Bureau, 74 percent of non-Hispanic whites are registered to vote in the United States. For African-Americans, that figure is 69 percent; for Hispanics, 57; and for Asian-Americans, 56. As the policy analyst Sean McElwee has noted, this means that even if every registered Latino voter in America went to the polls last November, Latinos’ overall turnout rate still would have been lower than it was for whites (63 percent).

Embracing a more conservative economic agenda, however, would solve none of the Democrats’ problems. At a time of historic inequality, rampant corporate consolidation and environmental crisis, the case for more robust redistributive social programs and public-interest regulations is strong. When centrist Democrats claim that making such a case is electoral suicide, they reveal less about the American public’s stubbornly center-right convictions than about their own.